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"Doping carbon nanotubes with tetrachloroaluminate ions can increase their electrical conductivity around tenfold without harming the nanotube structures, researchers in Spain have shown. The research helps explain the chemistry of nanotube doping, and could potentially lead to applications such as lighter, stronger cables for electricity distribution. ...
exposed commercial double-walled carbon nanotubes with an initial conductivity of around 1.4MS/m to an atmosphere of aluminium trichloride and excess chlorine for 24 hours, causing tetrachloroaluminate ions to diffuse into the structure. Spectroscopic analysis indicated that, rather than entering the nanotubes’ centres, the ions intercalated between the walls. The researchers observed no significant expansion of the nanotubes. They showed that the fact that the nanotubes are wrapped concentrically creates a greater gap between the carbon atoms than in multilayer graphene, ... ‘Therefore, it can host the dopant without distorting the bundle.’ ..."
From the editor's summary and abstract:
"Editor’s summary
Translating the outstanding individual properties of carbon nanotubes, such as their electrical and thermal conductivity, into bulk materials that retain those properties remains a challenge.
de Isidro-Gomez et al. demonstrated controlled vapor-phase intercalation of tetrachloroaluminate (AlCl₄−) ions within intertube channels to make macroscopic double-walled carbon nanotube fibers.
The fibers showed high electrical conductivity approaching 40% of the value of copper at room temperature.
On a per-weight basis, the cables exceeded both the conductivity and strength of conventional overhead cables. Furthermore, they showed excellent dry stability and reasonable moisture tolerance when protected by a polymer sheath. ...
Abstract
Translating the conductivity of individual carbon nanotubes into practical, macroscopic conductors remains a challenge.
We report highly aligned fibers of double-walled carbon nanotubes intercalated with chains of tetrachloroaluminate anions (AlCl4−) in the intertube channels. The AlCl4− intercalant acts as a noncovalent dopant, accepting 0.65 electrons per anion, mostly from the outer nanotube layer.
Combined with a 17% intercalant volume fraction, it produces an increase in room-temperature conductivity to values as high as 24.5 mega-Siemens per meter, which is 41% of that of copper.
Specific conductivity values reach 17,345 Siemens-meter squared per kilogram, which is superior to that of metals.
These fibers are five times stronger and half the weight of conventional overhead cables while remaining stable in dry conditions and retaining 80% of their conductivity protected from moisture by a cable polymer sheath."
Intercalated carbon nanotube fibers with high specific electrical conductivity (no public access)
The tetrachloroaluminate ions are positioned in interstitial channels between the double-walled carbon nanotubes
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